1. Field of the Invention
Embodiments of the present invention relate to resolving collisions in requests for setting up a direct link path between two stations in a wireless local area network.
2. Relevant Background
A 802.11 network is comprised of four primary components. These components include stations, access points, a wireless medium and a distribution system. The network is built to transfer data between stations. Stations include computing devices with wireless network interfaces. Laptop computers and handheld devices are examples of such devices. In some environments stations within a network are connected by wireless Local Area Networks (“LANs”). The 802.11 LAN standard is fast becoming the de facto standard for linking consumer electronics.
A frame on the 802.11 network must be converted to another type of frame to be delivered to a different type of network. This conversion is accomplished at an access point. Thus access points act to perform a wireless to wired bridge as well as numerous other functions. To move frames between access points the 802.11 network uses a wireless medium. The medium is controlled by a Medium Access Control (“MAC”) layer. The MAC layer is complemented generally by a physical layer and a data link layer.
Wireless networks face a number of challenges that are distinct from the traditional wired network. One such challenge includes frame collisions resulting from what is know in the art as a hidden node. FIG. 1 shows three stations 110, 120, 130 of a simplified wireless LAN. In addition the reachable area 115 by station 1 110 and the reachable area 135 by station 3 130 are shown. From the perspective of station 1 110, station 3 130 would be hidden and in the same manner from the perspective of station 3 130, station 1 110 would be hidden. Thus a simply “transmit and pray” protocol may result in station 1 110 and station 3 130 transmitting simultaneously rendering station 2 120 incapable of responding. Said another way, the transmissions by station 1 110 and station 3 130 collide.
Collisions of this type can be resolved by sending “request to send” and “cleared to send” signals. Thus in a typical scenario a station would issue a request to send signal and await for a clear to send signal from each station within the requestor's reach. Upon gaining a clear to send signal the frame would be transmitted. Thereafter the receipt of the frame would be acknowledged. The clear to send signal also serves to silence other stations that gain its receipt. Thus in FIG. 1 had station 1 110 sent a request to send signal and thereafter received a cleared to send signal in return from station 2 120, station 3 130 would have also received the message that station 1 110 was cleared to send. Station 3 130 would then remain silent until it received the acknowledgment signal from station 2 120 indicating the risk of collision had passed.
While by using this method the collision is resolved, the resolution comes at the price of increased latency and decreased efficiency. A similar type of challenge exists with respect to establishing a tunneled direct link between stations via an access point. In a 802.11 wireless network, network layer protocols are conveyed using logical-link control encapsulation. One type of encapsulation is called tunnel encapsulation. FIG. 2 shows a three step process for establishing a contention based direct link between two stations as is known to one skilled in the art. In the example shown in FIG. 2, station 1 210 desires to establish a direct tunneled link with station 2 220. The conventional means to establish a tunneled direct link is via a three-way handshake using an access point as an intermediary.
Initially station 1 210 sends a Tunnel Direct Link Setup (“TDLS”) request 230 to station 2 220 via the access point 215. Once received, station 2 220 responds to station 1 210 with a setup response 240. The setup response 240 causes station 1 210 to initiate a setup reply 250, which upon receipt by station 2 220 establishes the direct tunneled link. As can be appreciated by one skilled in the art, this three step process occurs over a finite period of time.
A problem occurs when both station 1 210 and station 2 220 attempt to set up a direct tunneled link at substantially the same time. In such a situation both stations 210, 220 act as initiator stations resulting in multiple collisions. Furthermore when security protocols between stations are required in the direct link setup path there are two sets of security parameters making it difficult to ascertain a master key or to begin the process to gain access to a temporary session key. These and other challenges existing in the prior art are addressed by the present invention, which is described hereafter by way of example.